Speed-reducing coupling

ABSTRACT

Disclosed is a device for coupling a rotary input of a first speed to a load which utilizes the input at a reduced speed, and wherein apparatus embodying the principles of a harmonic drive are combined with novel adjustable restraining elements and coupling means between the input and output of the apparatus to provide a speed-reducing coupling which has great strength, is simple, is inexpensive, and delivers smooth and continuous, vibrationless motion to the load.

United States Patent 1 1 Brown [451 Apr. 10, 1973 SPEED-REDUCINGCOUPLING [76] Inventor: Henry C. Brown, 410 Crusader Drive, Dallas, Tex.75217 [22] Filed: Feb. 4, 1971 [21] Appl. No.: 112,749

[52} U.S. Cl ..74/804, 74/243 R [51] Int. Cl ..F16h 1/28 [58] Field ofSearch ..74/804, 243 R [56] References Cited UNITED STATES PATENTS3,307,434 3/1967 Kope ..74/804 FOREIGN PA'IEIITS OR APPLICATIONS 961,0526/1964 Great Britain ..74/804 Primary ExaminerCv J. Husar Attorney-JamesD. Willborn [5 7] ABSTRACT Disclosed is a device for coupling a rotaryinput of a first speed to a load which utilizes the input at a reducedspeed, and wherein apparatus embodying the principles of a harmonicdrive are combined with novel adjustable restraining elements andcoupling means between the input and output of the apparatus to providea speed-reducing coupling which has great strength, is simple, isinexpensive, and delivers smooth and continuous, vibrationless motion tothe load.

11 Claims, 8 Drawing Figures PATEEJTEU 3,726,158

FIG. 2

E CCENTRIC Q l SHAFT q INVENTOR HENRY C. BROWN ATTORNEY PATENTEU 0575 I3,726,158

SHEET 2 BF 4 9 4 2, mmv 25 l3 FIG. 3

50A INVENTOR HENRY C. BROWN FIG. 4

ATTORNEY SHEET 3 [1F 4 FIG. 6

INVENTOR.

HENRY C. BROWN ATTORNEY PATEE'STEG 3.726.158

SHEET u 0F 4 ZlB-l 0 16 ECCENTRIC [NVENTOR HENRY C. BROWN 9,03%

ATTORNEY SPEED-REDUCING COUPLING This invention relates to mechanicalmovements and, more particularly, to harmonic drive speed-reducingcouplings.

Harmonic drive speed-reducers have been known and have been in use formany years. Some typical examples (which are illustrative of the lesscomplicated forms of this type of machine) are shown and discussed inthe material found and discussed at page 340 of Volume I, IngeniousMechanisms for Designers and Inventors, The Industrial Press, New York,N. Y., and at page 323 of Volume II of the same work. Through theirsimplicity, these speed-reducers appear to offer a high degree ofreliability, low initial cost and low maintenance costs. Unfortunately,however, these machines, in their simplified form, have never provenpractical for industrial applications.

The machines of the examples achieve speed reduction through the use oftwo planetary gears, rather than the four which would otherwise berequired to have the output aligned with and rotating in the samedirection as the input. The basic design suffers, however, because thereis a high degree of wear concentrated on the teeth of the input. andoutput planetary gears, where they mesh. This wear results in anever-increasing amount of backlash which appears in the output of thedevice as vibrating and pulsating motion, thus rendering the machineentirely unsuitable for many industrial applications.

Additionally, the driving teeth in any harmonic drive are heavilystressed, since only a relatively few teeth on the input planetary gearare normally in mesh with the output teeth at any one time, thus theload is concentrated. The constant and high degree of wear as sociatedwith the teeth, coupled with the high stress, tends to cause the teethto break and shear off, thus resulting in increased maintenance.Further, as more parts are added to the structure in an attempt toovercome these problems, especially those relating to the restrainingmechanism, the machine tends to become larger and less compact.Compactness is often a desirable or an essential requirement of aspeed-reducing coupling.

Therefore, it is an object of this invention to provide an improvedharmonic drive speed-reducer.

A further object is to provide an improved harmonic drive speed-reducerhaving a simplified structure for producing a smooth and continuous andrelatively vibrationless output.

Another object is to provide a harmonic drive speedreducer of a designwhich provides for reduced wear at critical points.

Still another object is to provide a harmonic drive speed-reducer of adesign which includes improved load-handling capabilities.

An additional object is to provide a compact harmonic drivespeed-reducer through the use of im proved, compact restraining means.

A still further object is to provide a harmonic drive speed-reducerwhich is adaptable for use in either high stress or miniaturizedapplications.

Other objects and advantages will be apparent from the specificationsandclaims and from the accompanying drawings illustrative of the invention.

In the drawing:

FIG. 1 is a partially sectioned side view of an embodiment of thisinvention.

FIG. 2 is a partially sectioned side view of the embodiment of FIG. 1,with the input shaft and sprocket rotated counter-clockwise.

FIG. 3 is a view in partial vertical section of a portion of theembodiment of FIG. 1, taken along the lines 3- 3.

FIG. 4 is a partially sectioned side view of another embodiment of thisinvention.

FIG. 5 is a view in partial vertical section of the embodiment of FIG.4, taken along the lines 55.

FIG. 6 is a top view of a portion of the apparatus for coupling theinput to the output of the embodiment of FIG. 1.

FIG. 7 is a partially sectioned side view of still another embodiment ofthis invention.

FIG. 8 is a view in partial vertical section of the embodiment of FIG.7, taken along the lines 7-7.

Referring now to FIG. 1, a housing 10 is securely fastened to ground 11so that it does not rotate or move with respect thereto. An input shaftmount 13 extends through a first wall 10-1 of the housing 10 and issecurely fastened to the housing, as with bolts or clamps (not shown).The mount 13 has a first end 13-1 positioned outside the first wall10-1, a second end 13-2 positioned inside the housing 10, and has a bore14 communicating with the first and second ends. The bore 14 has acircular cross-section and has a first portion 14-1, adjacent the firstend 13-1, which has a smaller cross-section than that of the portion14-2, adjacent to the second end 13-2. The bore 14 has a longitudinalaxis, as does each portion 14-1 and 14-2 thereof, and the longitudinalaxis of each portion is coincident with the longitudinal axis of thebore. A wall 16 joins the respective portions of the bore 14 and issubstantially perpendicular to the longitudinal axis thereof.

An input shaft 12 having a circular cross-section extends through thebore 14 and has a first end 12-1 coupled to a prime mover (not shown)and has a second end 12-2 positioned inside the housing 10, beyond thesecond end 13-2 of mount 13. The longitudinal axis of the shaft 12coincides with the longitudinal axis of the bore 14. A roller-bearing 15is positioned in the bore 14 axially of the shaft 12, adjacent to thewall 16.

An eccentric member 18 is located on the shaft 12, opposite a thrustwasher 17 from the mount 13. A first end portion of the eccentric member18 is cylindrically shaped and is located adjacent to the thrust washer17 and, in a plane perpendicular to the longitudinal axis of the shaft12, has a circular cross-section. The second end portion of theeccentric member 18 is also cylindrically shaped and, similarly, has acircular cross-section which lies in a plane which is perpendicular tothe longitudinal axis of the shaft 12; however, the cross-section at thefirst end is larger in diameter than that of the second end. The centerof the second end is offset a distance d from the center of the firstend-portion,

which center is in register with the longitudinal axis of the shaft 12,thus the portion of the member 18 adjacent the second end forms aneccentric with a throw of d, while the portion of the member nearest thefirst end thereof forms a cylindrically shaped spacer with the centercoinciding with the longitudinal axis of the shaft 12. A wall joins thefirst end-portion to the second end-portion of the member 18 and issubstantially perpendicular to the longitudinal axis of the shaft 12.The

wall extends around the periphery of the member 18, thus the radius ofthe second end (from its center) is greater than the distance d.

The first end-portion of member 18 fits into, in a spaced relationshipwith the side thereof, the second portion 14-2 of the bore of mount 13.The wall joining the respective portions of member 18 is spaced from thewall joining the respective portions of the bore 14 a distance such thatas member 18 is positioned against the thrust washer 17 and the washeris positioned against the joining wall 16 of bore 14, the wall joiningthe respective portions of member 18 is spaced along the longitudinalaxis of shaft 12 into the interior of housing further than is the distalend of the second end of mount 13. The shaft 12 is held in place withrespect to mount 13 by a bearing 15 and rotates about .its longitudinalaxis with respect to the mount.

A circular bearing 19 is positioned on an eccentric surface 26 of member18, and an input sprocket 20 is similarly positioned onto the bearing,thus the bearing 19 is constructed such that the eccentric 26 rotateswith the shaft 12 when motion of the sprocket 20 is restrained. Thesprocket 20 does not rotate, but nutates only, in responseto theeceentrics motion, as will be explained the following material.

The input sprocket 20 functions as a planetary gear having asubstantially circular cross-section in a plane perpendicular to thelongitudinal axis of the shaft 12 and having a surface 20-1 parallel tothe plane and facing the wall 10-1 of the housing 10. In thisembodiment, the sprocket 20 has a finite thickness which is small withrespect to the diameter thereof, and the sprocket has iterative teeth 21located around its periphery. The ratio of the number of teeth 21 on theinput sprocket 20 and the number of teeth 46 on the output sprocket (tobe described) are determinative of the speed reduction to be obtained bythis device, and there may be an even or an odd number of teeth oneither sprocket.

Two cam followers 22 are fixed to the input sprocket 20. Each camfollower 22 is a cylindrically shaped, elongate member having first andsecond ends and each has a longitudinal axis which is substantiallyparallel to the longitudinal axis of the shaft 12. The first end of eachcam follower 22 is secured to the sprocket 20 (as by threaded fasteners)and the second ends of the cam followers are each positioned between thesprocket 20 and first wall 10-1 of the housing 10. Additionally, thesecond end of each cam follower 22 has a roller bearing arrangedadjacent to the second end, circumferentially of the longitudinal axisof the follower, the outer surface of the bearing being the surface tocontact the cam race to be hereinafter described. The

cam followers 22 are spaced apart and, preferably, are

respectively positioned on opposite sides of the input shaft 12 and on astraight line lying on the surface 20-1 and intersecting thelongitudinal axis of the shaft.

Referring now to FIGS. 1 and 3, a pair of cam-members 24 are fixed tothe first wall 10-1 of housing 10, adjacent to and on opposite sides ofthe input shaft mount 13 and each in register with a respective camfollower 22. Each cam-member 24 has located therein, in register with arespective cam follower 22, a bore which forms a cam race 23. Each borehas a circular cross-section in a plane perpendicular to thelongitudinal axis of the cam follower 22, thus the cam race is circularin configuration, with the wall of the bore forming the surface incontact with a respective camfollower 22. In this embodiment, the boreforming the cam race 23 does not extend completely through the cammember 24, but is bottomed at a point within the member which is spacedfrom the second end of the cam follower 22.

Adjusting screws 27 are shown in FIG. 3 and provide a means foradjusting the position of each cam race. As will be discussed in thematerial which follows, the point of contact of each cam follower 22with its respective cam race 23 and the point of contact of therespective tooth 21 with the coupling means 50 forms a force trianglewith respect to each tooth. The diameter of each cam race 23 is exactlytwice the throw d of the eccentric 26, plus the diameter of the camfollower 22 and the throw and diameter of each race are related to thepitch of the teeth 21 such that each cam follower 22 is in contact witha respective cam race 23, while simultaneously at least one tooth 21 isin contact with a respective link of the coupling means 50 (to bedescribed), thereby forming the force triangle. It is desirable for thepurpose of having a smooth and continuous output of the speed-reducer 10to have the force.triangle transferred smoothly to successive teeth onthe input sprocket 20. The cam races and other components of the inputmechanism are machined to tolerances which aid in the desired transfer;however, as a matter of convenience and, consistent with the objectiveof providing a low-cost, high-performance embodiment, the cam races 23are made adjustable through the use of screws 27 which can be loosenedto accommodate the precise positioning of the cam member 24. Themounting holes in cam member 24 are also made over-size to accommodatethis adjustment. The cams 22-23 are always, therefore, in precisecontact, no matter which tooth 21 is engaged, thus backlash in therestraining mechanism, and between the input and output of the coupling10, is substantially eliminated.

In FIG. 1, the output shaft 28 extends through a bore 34 through asecond wall 10-2 of the housing 10. The output shaft 28 has alongitudinal axis which is in register with and is aligned with thelongitudinal axis of the input shaft 12.

An output shaft mount 29 is positioned in the bore 34. The mount 29 hasa bore 35 extending therethrough, and the bore has a longitudinal axisin register with the longitudinal axis of shaft 28. An output bearing33, similar to the bearing 19, is positioned in the bore 35, and theoutput shaft 28 is positioned in the bearing 33 such that the shaftrotates with respect to the mount 29. A retaining plate 32 has a bore32-1 at substantially the center thereof and the bore is large enough toaccommodate the shaft 28 without interference. The plate 32 is fastenedto the housing 10 with screws 31 which also pass through the mount 29'toposition and hold the mount and thus the shaft 28 in place in the bore34. additionally, the retainer 32 has an offset 36 machined in a facethereof and communicating with the bore extending through the centerthereof. The offset is positioned adjacent to the bearing 33 as themount 29, retainer 32 and bearing 33 are assembled and fastened to thehousing 10. The edge of the offset 36, which is opposite the center boreof retainer 32 is spaced from the bore a distance which places the faceof the retainer 32 in contact with the outside guide of bearing 33, thuspreventing any movement of the bearing outwardly along shaft 28, whileat the same time providing clearance between the retainer and otherportions of the bearing such there is no interference with the normaloperation of the bearing.

The output shaft 28 has a first end 38 and a second end 39. The shaft 28has a circular cross-section at the first end 38, a larger circularcross-section at the second end 39, and a wall 40 joining the first endto the second end. The wall 40 is substantially perpendicular to thelongitudinal axis of the shaft 28.

The wall 40 is positioned against the inner race of the bearing 33 andon a side opposite to the retainer 32 to prevent movement of the shaft28 outwardly of the housing 10.

The second end 39 has a bore 41 which extends inwardly along thelongitudinal axis of the shaft 28 toward the first end 38 thereof. Thebore 41 has a circular cross-section which is larger in diameter thanthat of the input shaft 12 and extends into shaft 28 a distance whichwill accommodate a bearing 42 and shaft 12 without interferencelongitudinally. Bearing 42 is positioned in the bore 41 between theshaft 12 and the wall of the bore.

An output sprocket 30 is fixed to the output shaft second end 39. Thesprocket 30 has teeth 46 extending outwardly from the longitudinal axisof the shaft 28. The sprocket 30 is secured to the shaft 28 by means ofa standard spline and key arrangement 43. A lock screw 45 holds thesprocket 30 and key 43 in position to prevent their movement along thelength of the shaft 28. The spline 43 also locks the sprocket 30 to theshaft 28 such that rotary motion imparted to the sprocket willcorrespondingly rotate the shaft. Additionally, the center of thesprocket 30 is in register with the longitudinal axis of the shaft 28and the teeth 46 are concentric with and equally spaced therefrom.

The second end 12-2 of the input shaft 12 is positioned within thehousing and within the bore 41 of the second end 39 of shaft 28. Athrust washer 44 is positioned on shaft 12, between the second end 39 ofshaft 28 and the eccentric 18. Eccentric 18 is secured to shaft 12 byspline 25 and is spaced from the second end of shaft 12 such thatmovement of the shaft 12 iongitudinally into the housing 10 brings theeccentric into contact with the thrust washer 44, the washer 44 intocontact with the second end 39 of shaft 28, wall 411 into contact withthe bearing 33 and bearing 33 into contact with retainer 32 to preventfurther movement of the shaft 12. When the shaft 12 is in this position,the end of the shaft is spaced from the bottom of the bore 41 to preventinterference therewith.

Movement of output shaft 28 longitudinally into the housing 10 bringsthe second end 39 thereof into contact with thrust washer 44, which, inturn, contacts eccentric 18, which contacts thrust washer 17, whichcontacts mount 13; thus, longitudinal movement of either shaft 12, 28(and thus of the sprockets and 30) is restricted in either directionwhile the teeth of the sprockets 20 and 30 are free to rotate about therespective shafts 12, 28, substantially in their respective planes.

A coupling means 50 (see FIG. 6 also) having a first channel 48 and asecond channel 47 is arranged around the periphery of the outputsprocket 30, and each link of the first channel 48 is in mesh with arespective tooth 46 thereof. Each link of each channel includes pins 51which traverse the length of the means 50 to form pivots which haverollers 52 positioned thereon. Each roller 52 is free to rotate aboutthe axis of the pin 51. The second channel 47 extends outwardly from theoutput sprocket 30, toward the first wall 10-1 of the housing 10, and isarranged in register with the teeth 21 of the input sprocket 20. Eachroller 52 and each corresponding channel 47, 48 are wide enough toaccommodate the teeth 21, 46 of the respective sprockets, with which thelinks are in register.

The specific means of securing coupling means 50 to the output sprocket30 is not material to this invention. It is only significant that themotion imparted to channel 47 by sprocket 20 be transmitted smoothly tothe output shaft. Whatever means are used should be rigid and free ofbending or backlash at the pressures applied. For instance, pins 51could be secured to the face and around the periphery of an outputsprocket, similar to 30, but having a circular cross-section with noteeth. Rollers, such as 52, could be mounted on the pins 51 andretaining means similar to the coupling linkage of coupling means 50could be added to create a second channel similar to channel 47.Additionally, rollerbearings could be added to such a second channel tofurther reduce the friction if this were required for a particularapplication. Coupling means of this type,

while having certain advantages, would undoubtedly increase the cost ofthe unit and would be a more difficult unit to maintain with respect tothe roller-chain embodiment described above.

Each tooth of the output sprocket 30 is in mesh with a respective linkof channel 48 of chain 50 at all times, while at least one of the teeth21 of the input sprocket 20 is in contact with a respective link ofchannel 47 of chain 50 at all times. While the at least one tooth 21 isin full contact with a link of channel 47, teeth 21 on the opposite sideof the sprocket 20 from the at least one tooth are not touching thecoupling means.

FIG. 2 illustrates the speed-reducing coupling of FIG. 1 with the inputsprocket 20 rotated counterclockwise with respect to its position asshown in FIG. 1.

FIG. 3 is a sectioned view of FIG. 2, showing the positioning of thecams 22 within the races 23, as the shaft 12 has been rotated. Further,this FIG. provides a better view of the means for adjusting the positionof the cam member 24. The bolts 27 extend through the cam number 24 andfasten to the wall 10-1 of the housing 10. Holes are provided at eitherend of the cam member 24 for accommodating the bolts 27. These holes aremade slightly larger than the outside diameter of the body of arespective bolt 27, for instance, for a three-sixteenths inch bolt, aone-quarter inch hole would be used. The oversized holes provide a meansfor loosening the screws 27 and relocating the member 24 to compensatefor errors in the machine tolerances and positioning of the cam races23, as previously described.

Referring to FIG. 4, a second embodiment of the harmonic drive of thisinvention is shown. In this embodiment the housing (FIG. 1) is notrequired and can be eliminated. In order to facilitate the description,the components of this embodiment are numbered corresponding to the sameof similar parts of FIG. 1, followed by the suffix A (or suffix B, inthe case of FIGS. 7 and 8). The configuration of the correspondinglynumbered parts is substantially the same as that of the parts of FIG. 1,unless otherwise specified.

As with the embodiment of FIG. 1, the input shaft 12A is coupled todrive apparatus (not shown) for imparting rotational motion to theshaft, the speed of which is to be reduced at the output shaft 28A andapplied to a load (not shown).

Eccentric member 18A has a flange 62 machined thereon and locatedbetween the eccentric surface 26A and the drive apparatus. A bearing 19Ais fit onto the eccentric surface 26A, and the eccentric is secured toshaft 12A by a standard spline and key arrangement 25A. The bearing 19Afits tightly on the surface 26A such that at least the inner race of thebearing rotates with the eccentric. A sprocket 20A is then fit in asimilar manner on the outer race of the bearing 19A, such that the shaft12A and member 18A rotate in response to the rotational input motionapplied to the shaft. The sprocket 20A nutates, but does not rotate,when rotational motion of the sprocket is restrained, as by the camarrangement to be described. The flange 62 is in contact with andrestrains movement of the bearing 19A along the axis of the shaft 12A inthe direction of the drive apparatus. A face of the flange 62 extendsoutwardly and perpendicularly from the shaft 12A, beyond the eccentricsurface 26A and contacts a side of the inner race of the bearing 19A toprevent such movement.

A spacer portion 60 is machined onto the shaft 12A, spaced from thesecond end 61. The spacer 60 has a first shoulder which is perpendicularto the longitudinal axis of the shaft 12A and is spaced from the secondend 61 thereof. A bearing 33A is positioned on the shaft 12A, adjacentto the second end 61. The inner race of the bearing 33A is in contactwith the first shoulder, thus movement of the bearing away from thesecond end 61 and along the shaft 12A is restrained. Additionally, thespacing between the first shoulder and the second end 61 corresponds tothe width of the bearing 33A, thus the bearing does not extend outwardlyfrom the shaft, beyond the second end. An eccentric 26A is positioned onthe shaft 12A on the opposite side of the spacer 60 from the second end61 and against a second shoulder thereof which is similar inconfiguration to the first. The eccentric 26A is secured to the shaft12A by a spline and key arrangement A. The shape and configuration ofeccentric member 18A is substantially the same as that of eccentric 26of FIG. 1, except for the bearing retainer or flange 62 just described.

The output shaft 28A has a longitudinal axis which is in register withand is aligned with the longitudinal axis of shaft 12A. A first end ofthe output shaft 28A is coupled to a load, and the second end ispositioned in close proximity to the second end 61 of the shaft 12A. Anoutput sprocket 30A has a face 64 which is substantially perpendicularto the longitudinal axis of the shaft 28A and has an end 65, oppositethe face 64.

The sprocket 30A has a bore with a circular crosssection located at thecenter thereof and communicating with the face 64 and the end 65. Thebore has a first portion adjacent the end 65 which is substantially thesame diameter as the shaft 28A and mates therewith, with the shaft beingpositioned in the bore and secured thereto by a spline and keyarrangement 43A. The second portion of the bore extends from the firstportion to the face 64 and has a slightly larger diameter. The wallconnecting the first portion to the second portion is substantiallyperpendicular to the longitudinal axis of the shaft 28A. The diameter ofthe second portion corresponds to the outside diameter of the bearing33A.

The second end of the shaft 28A does not extend into the second portionof the bore, but the bore second portion is of sufficient length toaccomodate the full width of the bearing 33A. The bearing 33A is fitinto this portion of the bore and has one edge positioned against theshoulder separating the bore first and second portions and has itsopposite face in register with the face 64.

It can now be seen that as the shafts 12A and 28A are placed intoposition, the inner race of bearing 33A rests on the shaft 12A, and theouter race of this bearing is in contact with the bore of sprocket 30A.In this position, the sprocket 30A and shaft 28A are free to rotatetogether with respect to the shaft 12A, but are held in a fixed axialalignment with respect thereto by means of the bearing 33A. Shaft 28A ispositioned in the bore of sprocket 30A such that when the bearing 33A,sprocket 30A, shaft 12A and shaft 28A are in place, there is a nominalclearance between the end of shaft 28A and the end 61 of shaft 12A, suchthat there is no actual contact between these members.

The sprocket 20A has teeth 21A positioned around the periphery thereof.While this is not necessarily true of the embodiment of FIG. 1, theinput sprocket of the device of FIG. 4 must have an even number of teethon the input sprocket, for instance, in the embodiment shown, the inputsprocket 20A has 18 teeth. Correspondingly, the output sprocket 30A ofFIG. 4 must also have an even number of teeth, in this case 20.

A major difference between the embodiment of FIG. 4 and that of FIG. 1exists in the cam arrangement. The cam follower 22A is substantially thesame as that of cam follower 22 of FIG. 1, and the cam race 23A issubstantially the same as cam race 23 of FIG. 1; how ever, cam race 23Ais secured to a face 64 of the output sprocket 30A with screw fasteners,such as 63, rather than to a housing such as housing 10 as in FIG. 1. InFIG. 4, the cam follower 22A has its position reversed with respect tothe position of cam 22 (FIG. 1), in that the cam 22A extends outwardly,away from a face of input sprocket 20A and toward the output sprocket30A and the cam member 24A and cam race 23A are secured to the face 64thereof. The spacing between the input sprocket 20A and output sprocket30A, determined by the width of spacer 60, is such that the cam follower22A engages the cam race 23A, but the distal end of the cam does notcome into contact with any portion of sprocket 30A or cam member 24A,except the cam race.

A portion of each cam member 24A extends outwardly into the bore ofsprocket 30A and into contact with the bearing 33A, thus securing thebearing 33A into place between the respective cam members 24A and theshoulder separating the first and second portions of the bore throughsprocket 30A.

The output sprocket 30A in the embodiment shown has 20 teeth locatedaround the periphery thereof. A coupling means 50A, similar inconstruction to the coupling means 50 of FIG. 1, is positioned on theoutput sprocket 30A, with one link of one channel corresponding andcoupling to each tooth thereof. The second channel of the coupling means50 is in register with the teeth 21A of the input sprocket 20A and incontact with at least one of these teeth.

The diameter of the input sprocket 20A is less than that of the outputsprocket 30A by an amount equal to the throw d of the eccentric 26A,thus at least one of the teeth of the input sprocket is always in fullmesh with the second channel of the coupling means 50A and several otherteeth are in partial mesh therewith.

In this embodiment there are two cams 22A and two cam races 23A. Refernow to FIG. wherein it is shown that the center of the circular camraces 23A are positioned with respect to the sprocket 30A on oppositesides of the shaft 12A and bearing 33A and on a straight line whichpasses through the longitudinal axis of the shaft 12A. Preferably, thecenter of the respective races 23A are aligned under a respective tooth46A of the output sprocket 30A. Similarly, the center of cams 22A arearranged on the input sprocket 21A in a corresponding manner. Each cammember 24A is secured to the output sprocket 30A by means of bolts, suchas 63. A hole is bored through the sprocket 30A to accommodate each bolt63, and each is made larger in diameter than the bolt, as described inrespect to the bolts 27 of FIG. 1, to allow room to adjust the positionof the cam member 24A.

' Still another embodiment of this invention is shown in FIGS. 7 and 8.In this embodiment the input shaft 12B has a longitudinal axis and aneccentric 52B is machined on the input shaft and offset as described forother eccentrics (FIG. 1 and FIG. 4). Between the input shaft 128 andthe eccentric 52B are threads 71, and on the opposite side of theeccentric from shaft 128 is a shoulder 72, which separates the eccentric52B and a portion of the input shaft 82 which has a larger diameter thanthat of the eccentric 528. On the opposite side of the portion 82 fromthe eccentric 52 is a second portion of the input shaft 83 which has ashoulder 75 located on a side opposite the eccentric. The shoulders 72and 75 are plane surfaces which are substantially perpendicular to thelongitudinal axis of the input shaft 12B, and shoulder 75 joins shaftportion 83 with shaft portion 84. Shaft portion 84 has a substantiallysmaller diameter than that of the eccentric shaft portion 82 or shaftportion 83. The shaft portion 84 terminates in an end 85, and adjacentto the end 85 are threads 79, which are located on the outer surface ofthe shaft. Tapered input bearings 198-1 and 1913-2 are positioned on theeccentric surface 528 and held in position between shoulder 72 and aretaining nut 70 which is fastened on the shaft 12B by threads 71.

In this embodiment, the input sprocket 21B is formed of two distinctportions 218-! and 218-2 which are held together with bolts 73. Thefirst portion 218-! is cylindrically shaped and has a bore through thecenter and communicating with both ends thereof. The diameter of thisportion 218-1 is larger than that of the eccentric 528. The width of thesprocket portion 218-1 is substantially the same as the width of theeccentric 52B. Near the center of the bore of the sprocket first portion21B-1 is located a spacer 76 machined into the surface of the bore andlocated circumferentially around the bore. Each of the bearings 19B-1and 19B-2 are tapered roller-bearings of the type which are identifiedin TABLE I. Bearings 158-1 and 19B-2 are placed on the surface of theeccentric 52B, and are spaced apart by the spacer 76, with the innerbore surface of the sprocket portion 21B-1 riding on each of thebearings 1913-1 and 198-2 are turned in opposite directions, each facingthe spacer 76 and having its taper nearest the shaft 128 at the facingedges of the bearings.

The second portion 2lB-2 of the input sprocket is fastened to the firstportion 2lB-l by bolts 73. The second portion 218-2 has a bore at thecenter thereof having a diameter large enough to accommodate, withoutinterference, the shaft portion 82 as it nutates in response to motionof the eccentric 52B. Teeth 20B are located around the periphery of theinput sprocket portion 2lB-2 which has a larger diameter than that ofthe input sprocket portion 218-1.

Each of the bolts 73 coupling the respective sprocket portions 21B-1 and218-2 have located on the respective ends thereof, cam followers 228which extend outwardly from the face of the portion 21B-2 toward the end85 of the input shaft 128. The cam followers 228 are substantially thesame in construction and configuration as those cam followers 22 ofFIG. 1. The portion 83 of the input shaft 128 is slightly greater inwidth than the length of the cam follower 22B extending outwardly fromthe surface of the input sprocket second portion 21B-2.

The output sprocket 30B is of a slightly different configuration thanthat of the out sprockets shown in FIGS. 1 and 4, in that it has twoparallel rows of teeth 468-1 and 46B-2 located around the peripherythereof. The output shaft 28B is secured, as by welding 80, to an outputflange 81. The output flange 81 is secured to the output sprocket 30B bybolts 86. The longitudinal axis of the output shaft 28B is in registerwith the longitudinal axis of the input shaft 128. The output sprocket308 has, at the center and along the longitudinal axis thereof, a bore87, and the longitudinal of the output sprocket 30B is in register withthe output shaft 288 when the two are positioned together as described.

A spacer 77, similar to spacer 76 associated with the input sprocket21B, is located on the interioe of the bore 87. Bearings 338-1 and 338-2are placed in the bore 87 similarly to the arrangement of bearings 198-1,and 19B-2 associated with the input sprocket 21B.

Specifically, the shaft portion 84 is in register with the on the shaftportion 84, with both bearings being held in position by a nut 78 whichis fitted to the thread 79 at the end of the shaft portion 84. Thebearings 338-1 and 338-2 are tapered in opposite directions, similar toAll other parts are ASA Standard, as described, except the shafts 12,12A, etc. and their eccentrics, which are specially machined andprepared for the application described. By way of illustration, thethrow of a the arrangement of the bearings 198-1 and 1913-2 asrespectiveeccentric can be easily computed as follows. sociated with the inputspsocket 218. In FIG. 1, there are 19 teeth on the input sprocket 20 Camraces 24B are located on the surface of the outand 20 teeth on theoutput sprocket 30. The input put sprocket 30B, facing the inputsprocket 21B. The sprocket 20 has a bottom diameter (the diameter of theinput shaft portion 83 is wider than the maximum sprocket taken at thebottom of the teeth), B.I., which thickness of the cam races 24B suchthat there is no inis 2.725 inches. The bottom diameter of the outputterference between a respective cam race 24B and the sprocket 30, B. 0.,is 2.883 inches. The throw, thereinput sprocket portion 21B-2. Bolts 63Bextend fore, is given by the equation d (B.O.B.l.l2) or through theoutput sprocket 308 to hold the cam races 0.079 inches. 24B in position.The cam races 23B are in register with The ideal outside diameter of theinput sprocket (the the cams 22B, and are similar in construction to thediameter of the sprocket taken at the tip of the teeth), cam races 23shown and described with respect to FIG. 0. I., is computed as follows.1, The radius, I. N., of the input sprocket at the diame- The throw 1 0fthe eccentric 52B corresponds to the ter B. 1. equals B.l./2. Theradius, 1,, 0f the diameter 0. depth of the teeth 203 on th i t s rock tTh I. of the input sprocket should be the equal to the coupling means508 is what is commonly known as a diameter of outside sprocket, B. 0.,minus the radius 1,; triple roller-chain, having three channelsextending since the outside diameter 0. I. of the input sprocket isaround the periphery thereof and coupling back on ith, the Optimumdiameter, a, the diameter of the self to encircle the output sprocket30B. Each length of input Sprocket at the P of the teeth is the means503 couples with a respective tooth on the 25 output sprocket 308, forinstance 46B-l. As the chain is closed, the chain is effectively fixedto the output sprocket and will not move with respect thereto. One 1 HQ)Bl/2) X 2 or channel of the means 50B is in mesh with teeth 468-1 andthe second channel thereof is in mesh with teeth 468-2. The thirdchannel of the chain extends outwardly from the output sprocket 30B andis in register with the input sprocket 218-2. At least one tooth of them our example input sprocket 218-2 is in contact with the third channelof the chain 50B at all times. Aside from having 5 three channels ratherthan two, the means 508 is constructed in the same manner as the means50 of FIGS. 1 a 2-883 X 2 3-041 and 6. The bearing surface 523 of thethird channel of the means 508 rotates on the connection pin linkagejoining the three sections of the chain together.

In either of the embodiments described, the output sprocket and couplingmeans and their associated hard- Since the outside diameter 0. I. of theinput sprocket is ware are considered as output means, in the broadest3.30 inches (from mfg. catalog), 0.259 in. of material sense of theterm, i.e., means for coupling the motion of would have to be removedfrom the input sprocket the input sprocket to the output shaft and theload. teeth of the example. Other standard sprockets of dif- For theembodiments of this device described herein, ferent sizes, or involvingdifferent input to output ratios the off-the-shelf components are of thetype and mode or more or less teeth, may not have to be modified, butnumber described in the following table: the same clearance formulawould apply.

TABLE I Desig- Part nator Model No. Manulnctun-r Manufacturer addressBearing 15 13-1210 'lhc Torrinuton (2o A 'Iorrington, Conn. 06700.Thrust washcr A North American Rockwell, Boston Gear Division 14 HaywardSt., Quincy, Mass. 02171. Beaiigng Marlin-ltoukwell (30., Division of'IRW, lnc J2II'IIFESS80WII, New York 14701.

MRC R-12-ZZ McGillMl'g. ()0 'Iimken Roller Bearing Company MartinSnrockctdz (lcars, lnc

The Torrington Co Canton, Ohio 14700.

3106 Sprocket Drive, Arlington, 'li-xas.

CF-1/2 McGill Mfg. Co., Bearing Division. Valpariso, Indiana 40383.

CF-1/2 .-d0 Do.

401320 Martin Sprockl-t & (icars, lne 3106 Sprocket Drivc, Arlington,Texas. 60820 (1 Do.

Double-601320.. Do

MGR R-20-ZZ Jarngstown, New York 14701.

Torrington. Conn. 06790.

TB-1225 North American Rockwell, Boston Gear Division. 14 Hayward St.,Quincy, Mass. 021'71. ASA 40-2 Acme Chain Corporation Holyoke, Mass. ASA-2 do Do. Do. ASA 60-3 Cotter Boston Roller Chain 14 Hawyard St.,Quincy, Mass. 02171. Sprocket fiflAl.) Acme Roller Chain CorporationIIolyoke, Mass.

D0. 60AM) Martin Sprockct K: Gears, Inc 3106 Sprocket Drive, Arlington,Texas. Cam follower. 2213 CF-1/2 McGill Mfg. Co. hearing DivisionValpariso, Indiana 46383.

The operation of the basic nutating gear or harmonic drive is well-knownand is described in Volume I of Ingenious Mechanism for Designers andInventors at page 340 and in Volume III of the same work at page 323.

Fundamentally, the transfer of motion from the input to the outputsprocket is accomplished by introducing wabble or nutating motion to theinput sprocket and transferring this motion to the output shaft in theform of rotational motion.

Refer to FIG. 1. A prime mover is coupled to the first end of the inputshaft 12 and provides torque and rotational motion of the shaft at thatpoint. As the input shaft 12 rotates, the eccentric 26 rotates therewithand provides motion to the input sprocket 2]. Cam followers 22, inconjunction with the cam races 23, prevent the rotation of the inputsprocket 20 about the shaft 12, while allowing it to nutate or wabble inresponse to the motion of the eccentric 26. The axis of the inputsprocket 20 follows the motion of the eccentric 26, but does not rotateabout its own axis because of the cam and cam race arrangement 2223.

As the axis of the eccentric 26 rotates about the shaft 12, the innerrace of bearing 19 rotates therewith, while the outer race of bearing 19tracks the motion of sprocket 20. The earns 22 coupled to the cam racesupport 24 prevent the rotation of sprocket 20, but allows the sprocketto move vertically and horizontally a distance which is equal to thedifference between the diameter of the cam race 23 and the cam 22. Thus,this motion is imparted to each tooth around the periphery of the inputsprocket and at least one tooth, in contact with the coupling means 50,meshes fully with a link of coupling means 50, backs out of mesh andre-meshes with the next adjacent link of the coupling means dur ing eachrevolution of the input sprocket. This occurs with respect to aparticular tooth when the cam 22 is in contact with a point on the camrace 23 which corresponds .with the location of the respective tooth onthe periphery of the sprocket 20. A tooth 21 directly opposite to thetooth in contact will be clear of the coupling means 50.

As the shaft 12 rotates each one-nineteenth of a revolution, anothertooth engages the coupling means 50. During each one-nineteenth of therevolution, the motion of the sprocket 20 forces the respective toothoutwardly from the shaft 12, and into mesh with the respective link ofthe coupling means and, specifically, into contact with the surface 52which is free to rotate on the axis 51 of the respective link, thusserving as a roller bearing between the tooth and the link. As therespective tooth 21 is brought into contact with a respective link, thecoupling means 50 is rotated a finite degree. As this tooth is makingcontact, the next tooth is beginning to engage in a similar manner withits respective link, thus, it begins to impart motion to the couplingmeans 50 also. Successive teeth making contact in this manner inresponse to motion of the eccentric 26 provides rotary motion to thecoupling means 50. The second channel 48 of the coupling means 50 doesnot move with respect to the output sprocket 30, since each tooth 46 ofthe output sprocket is directly coupled to a link thereof. As previouslydescribed, the output sprocket is coupled directly to the output shaft28 which is in turn coupled to a load (not shown), thus the input iscoupled directly to the output through the coupling means 50, and therotary motion imparted to the coupling means 50 is transferred throughthe output shaft to the load.

In other nutating drive devices, the meshing of the input teeth with theoutput portion of the device subjects these teeth to intenselyconcentrated shearing forces and a very high wear factor resulting fromsliding friction. This has caused many machine designers to divert toother less direct coupling between the input and output, resulting inmore expensive, more com plex, less desirable drives. Through theaddition of the roller bearing 52 at the critical point of contact,tooth wear from sliding friction is substantially eliminated, while atthe same time, the basic simplicity of the direct drive device isretained in conjunction with all the inherent advantages of the lesscomplicated device.

Since the axis of the input sprocket 20 follows the motion of theeccentric 26 and the sprocket does not rotate about its own axis, themotion imparted to the driven sprocket 20 will be uniform and equal tothe speed of shaft 12 times (N-n/N), where N is the number of teeth inthe output sprocket and n is the number of teeth in the input sprocket.The reduction ratio for this device may be expressed by the equation R(N/N-n). Thus, if N equals 20 teeth and n equals 19 teeth, as in FIG. 1,the speed reduction ratio will be 20 to I. If N equals 20 teeth and nequals 18 teeth, then the reduction ratio will be 10 to 1. Similarly, ifN equals 20 teeth and n equals 16 teeth, the reduction ratio will be 5to l.

The positioning of the bearing 26 between the input sprocket 21 and theinput shaft 12 operates to reduce the amount of wear previouslyexperienced in the nutating gear drive apparatus, thereby greatlyextending the life of the present device. The cam 22 is constructed witha bearing between the sprocket 20 and the cam surface 22, againsubstantially reducing friction.

The cam races 24 are constructed to be adjusted by loosening theretaining screws 27 (FIG. 3). One of the major causes of vibration inharmonic drives is the operation of the restraining elements. In thisinvention, the diameter of the cam race is precisely coordinated withthe throw d of the eccentric 26 and the desired motion of the teeth 21to allow alternative meshing and disengagement of the teeth with thecoupling means 50. The bearing associated with the cam 22 substantiallyeliminates undesired wear, and with a circular cam race, the cam andrace are maintained in constant and uniform contact, thereby preventingthe vibration of other units using vertical or lateral cam races inconjunction with the restraining members. The cam 22 tracks the motionof the axis of the eccentric 26, and the motion of the axis of theeccentric 26 is uniform. The contacting surface of the circular cam race23 is precisely aligned and in contact with the cam 22 at all times,thus the uniform motion of the axis of eccentric 26 is passed through'adirect path from the eccentric 26, through the bearing 19, the sprocket20, the cam 22, the cam race 23 to the fixed ground 11. When the camrace supports 24, and thus the cam races 23, are properly aligned,vibration resulting from the backlash found in other devices can beeffectively tuned out of the present device.

The backlash is still further reduced in the embodiment described by theuse of more than one cam and cam race arrangement 22-23, and byproviding for adjustment of the position of the cam race 23 with respectto its ground and the motion of the axis of the eccentric. Because ofthis aspect of the machine, standard, off-the-shelf hardware can be usedin the construction of this harmonic drive and superior results inperformance can be obtained, while the cost of the unit isproportionately reduced. Expensive high-precision components are notrequired.

Since the wear associated with sliding friction between the input andoutput of the device has been substantially reduced, the gradual wear ofthe loadbearing teeth in the drive is reduced and the teeth lose theirtendency to shear under heavy loads.

Additionally, the restraining means, such as cam arrangement 22-23, donot require levers and linked mechanism for proper operation, thus thepresent device is more compact than devices having such arrangements.Also, the present device is particularly suitable for miniatureapplications, since all components can be easily reduced in size, andthe device is reversible for applications requiring that feature. In thepresent device the output always rotates in the same direction as theinput, which is still an additional advantage for many applications.

The embodiment of this invention shown in FIGS. 4 and 5 operates in thesame manner and has the same advantages as those of the embodiment ofFIGS. 1 and 2, except that it has the added advantage of being morecompact. In this embodiment, the restraining elements 22A and 24A areeffectively grounded to the output, i.e., the load, and the requirementfor a housing with fixed ground is eliminated.

The input shaft 12A and eccentric 26A are free to rotate free of theoutput because of bearings 19A and 33A. The input sprocket 20A nutatesin response to the motion of eccentric 26A. The cam race support 24A andcam race 23A are secured to the output sprocket 30A, and the motion ofthe input sprocket 20A in response to the rotation of eccentric 26A isalways relative to a fixed point on the output apparatus, thus thenutating input sprocket advances the coupling means 50A, the outputsprocket 30A and the output shaft 28A in the same manner as the deviceof FIG. 1. The advancement of the sprocket 30A rotates the cam racesupport 24A, but sprocket 20A and cam follower 22A track the cam race23A and the relative speed of the input sprocket to the output sprocketis not affected.

The cam race supports 24A can be adjusted to reduce backlash by means ofthe adjusting screws 63.

The embodiment shown in FIGS. 7 and 8 operates in substantially the samemanner and has the same advantages as the embodiment of FIGS. 4 and 5,except that this embodiment is designed with tapered bearings 19B and333. The bearings 19B-1 is grounded to the shaft 128 by nut 70 withprevents movement of the bearing along the axis of the shaft 12-B towardthe input. Similarly, bearing 19B-2 is fixed to the shaft 12B and itsmotion toward the end 85 of that shaft is prohibited by the shoulder 72of shaft portion 82. Both bearings 19B-l and 198-2 are retained in theserespective positions and fixed with respect to each other by the spacer76 of the input sprocket portion 218-1.

Similarly, bearings SIB-1 and 318-2 are arranged on the shaft 12B, butare held in position with respect to each other and with respect to theoutput shaft 288 by the shoulder 77 of the output sprocket 303.

With these bearings arranged in this manner the coupling 108 will takesubstantially higher laterally imposed loads, either from the input orthe output, without being damaged. A lateral load imposed along theinput shaft 128, into the coupling is impressed through shoulder ofshaft 128 on bearing 338-1, through bearing 33B-1 on spacer 77 ofsprocket 30B, from spacer 77 to bearing 338-2 and thence to nut 78. Inthis manner the internal spacing of the drive 10 is maintained, and theneed for thrust washers, such as 17 and 44 of FIG. 1, is eliminated. Inany application where the lateral forces are likely to be applied toeither the input or output shafts, the thrust washers are a source ofadded wear and friction, thus the bearings 19B and 33B arranged in thismanner provide a means for eliminating wear from lateral forces tofurther improve the coupling.

The double-sprocket 308 at the output of the device adds greaterstrength to the overall drive and provides a means for keeping thecoupling means 50B in alignment and in register with the teeth of theinput sprocket 218 when the drive 108 is subjected to lateral forces.

It is apparent that other variations and modifications may be madewithout departing from the present inven tion. Accordingly, it should beunderstood that the forms of the present invention described above andshown in the accompanying drawing are illustrative only and not intendedto limit the scope of the invention.

What is claimed is:

l. A speed-changing coupling comprising:

a first rotatable shaft;

a first sprocket eccentrically connected to the first shaft and havingmeans for driving movable orbitally about the axis of the shaft;

a second sprocket having a diameter larger than that of the firstsprocket and rotatable about the same axis;

coupling means fixedly secured to the periphery of the second sprocketand having a portion thereof in driven engagement with the driving meansof the first sprocket;

a pair of spaced, circular cam races secured to a surface of the firstsprocket, adjacent to the second sprocket;

a pair of circular cam followers secured to the second sprocket, eachdisposed to mate with and follow a respective one of the cam races; and

a second rotatable shaft coupled to the second sprocket.

2. The speed-reducing coupling claimed in claim 1 wherein the firstsprocket includes teeth at its periphery and the coupling means is acontinuous double chain, having first and second channels, said firstchannel being fixedly coupled to the second sprocket and said secondchannel being in register with the teeth of the first sprocket and indriven contact with at least one tooth thereof.

3. The speed-changing coupling claimed in claim 2 wherein each link ofat least the second channel of the double chain has associated therewitha roller bearing arranged to make contact with at least one tooth of thefirst sprocket as the first sprocket is rotated.

4. A speed-changing coupling comprising:

a rotatable input shaft;

an input sprocket eccentrically connected to the input shaft and havingteeth arranged to be movable orbitally about the axis of the shaft;

an output sprocket having a diameter larger than that of the inputsprocket and rotatable about the same axis;

a double-chain having one channel thereof secured to the periphery ofthe output sprocket and having a second channel thereof in drivenengagement with at least a portion of the teeth of the input sprocket;

at least one cam race having a circular cross-section secured to a faceof the second sprocket adjacent to the first sprocket;

at least one cam follower having a circular cross-section of a smallerdiameter than that of the at least one cam race secured to the face ofthe first sprocket and disposed to mate with the at least one cam race;and

output means coupled to the output sprocket for attaching the couplingto a load.

5. The speed-changing coupling of claim 4 wherein the at least one camrace is formed as a part of the second sprocket.

6. The speed-changing coupling of claim 4 wherein the at least one camrace is secured to the first sprocket and the at least one cam followeris secured to the second sprocket.

7. A speed-changing coupling comprising:

a housing having an internal surface;

a first shaft rotatably mounted in the housing;

a first sprocket eccentrically connected to the first shaft and havingteeth movable orbitally about the axis of the shaft, said shaft beingdisposed with respect to the internal surface;

a second sprocket having a diameter larger than that of the firstsprocket and rotatable about the same axis;

coupling means fixedly secured to the periphery of the second sprocketand having a portion thereof in driven arrangement with the teeth of thefirst sprocket;

a pair of spaced cam races secured to the internal surface of thehousing and each having a circular cross-section;

a pair of cam followers, each having a circular crosssection smallerthan that of the respective cam races secured to a face of firstsprocket and disposed to mate with a respective one of the cam races,and

output means coupled to the output sprocket for attaching the outputsprocket to a load.

8. The speed-changing coupling claimed in claim 7 wherein the cam racesare secured to the input sprocket and the cam followers are secured tothe internal surface of the housing.

9. The speed-reducing coupling of claim 1 wherein the cam races aresecured to the second sprocket and the cam followers are secured to thefirst sprocket.

10. The speed-reducing coupling of claim 1 wherein an eccentric havinfga throw d is dis osed between the first shaft and the irst sprocket andhe diameter of the cam race is equal to the diameter of the cam followerplus the throw d of the eccentric.

11. The speed-changing coupling of claim 1 wherein the cam races areformed as a part of the first sprocket.

1. A speed-changing coupling comprising: a first rotatable shaft; afirst sprocket eccentrically connected to the first shaft and havingmeans for driving movable orbitally about the axis of the shaft; asecond sprocket having a diameter larger than that of the first sprocketand rotatable about the same axis; coupling means fixedly secured to theperiphery of the second sprocket and having a portion thereof in drivenengagement with the driving means of the first sprocket; a pair ofspaced, circular cam races secured to a surface of the first sprocket,adjacent to the second sprocket; a pair of circular cam followerssecured to the second sprocket, each disposed to mate with and follow arespective one of the cam races; and a second rotatable shaft coupled tothe second sprocket.
 2. The speed-reducing coupling claimed in claim 1wherein the first sprocket includes teeth at its periphery and thecoupling means is a continuous double chain, having first and secondchannels, said first channel being fixedly coupled to the secondsprocket and said second channel being in register with the teeth of thefirst sprocket and in driven contact with at least one tooth thereof. 3.The speed-changing coupling claimed in claim 2 wherein each link of atleast the second channel of the double chain has associated therewith aroller bearing arranged to make contact with at least one tooth of thefirst sprocket as the first sprocket is rotated.
 4. A speed-changingcoupling comprising: a rotatable input shaft; an input sprocketeccentrically connected to the input shaft and having teeth arranged tobe movable orbitally about the axis of the shaft; an output sprockethaving a diameter larger than that of the input sprocket and rotatableabout the same axis; a double-chain having one channel thereof securedto the periphery of the output sprocket and having a second channelthereof in driven engagement with at least a portion of the teeth of theinput sprocket; at least one cam race having a circular cross-sectionsecured to a face of the second sprocket adjacent to the first sprocket;at least one cam follower having a circular cross-section of a smallerdiameter than that of the at least one cam race secured to the face ofthe first sprocket and disposed to mate with the at least one cam race;and output means coupled to the output sprocket for attaching thecoupling to a load.
 5. The speed-changing coupling of claim 4 whereinthe at least one cam race is formed as a part of the second sprocket. 6.The speed-changing coupling of claim 4 wherein the at least one cam raceis secured to the first sprocket and the at least one cam follower issecured to the second sprocket.
 7. A speed-changing coupling comprising:a housing having an internal surface; a first shaft rotatably mounted inthe housing; a first sprocket eccentrically connected to the first shaftand having teeth movable orbitally about the axis of the shaft, saidshaft being disposed with respect to the internal surface; a secondsprocket having a diameter larger than that of the first sprocket androtatable about the same axis; coupling means fixedly secured to theperiphery of the second sprocket and having a portion thereof in drivenarrangement with the teeth of the first sprocket; a pair of spaced camraces secured to the internal surface of the housing and each having acircular cross-section; a pair of cam followers, each having a circularcross-section smaller than that of the respective cam races secured to aface of first sprocket and disposed to mate with a respective one of thecam races, and output means coupled to the output sprocket for attachingthe output sprocket to a load.
 8. The speed-changing coupling claimed inclaim 7 wherein the cam races are secured to the input sprocket and thecam followers are secured to the internal surface of the housing.
 9. Thespeed-reducing coupling of claim 1 wherein the cam races are secured tothe second sprocket and the cam followers are secured to the firstsprocket.
 10. The speed-reducing coupling of claim 1 wherein aneccentric having a throw d is disposed between the first shaft and thefirst sprocket and the diameter of the cam race is equal to the diameterof the cam follower plus the throw d of the eccentric.
 11. Thespeed-changing coupling of claim 1 wherein the cam races are formed as apart of the first sprocket.